Electrical systems



Feb- 2, 1960 M. E. PARTIN ELECTRICAL SYSTEMS Filed DSO. 5, 1956 UnitedStates Patent O ELECTRICAL SYSTEMS Melvin E. Partin, Philadelphia, Pa.,assignor lto Philco Corporation, Philadelphia, Pa., a corporationoftPenn- Sylvania Application December 3, 1956, Serial No. 625,734

Claims. (Cl. 313-92) This invention relates to improvements in cathoderay tubes and in particular to improved screens for cathode ray tubesused to reproduce scenes `televised in colors.

There are systems for the reception of color television signals whichemploy a cathode ray tube having an image-forming, beam-interceptingstructure constituted in part of a screen having a plurality of setsoftstrips of phosphor materials which are disposed substantiallyparallel to one another. 'Each of the sets of phosphor strips emitslight of a particular color when bombarded by an electron beam. .Anelectron beam, Whose intensity is modulated by signals representativeAof 'the colors of the "scanned elements of a televised scene, is causedto scan :such structure in amanner such that, at a time when it ismodulated in intensity by a signal `representative of, say.the 'redcolored elements of the scene,itwill impinge only on a phosphor stripemissive of `red light. The Astrips are :made very line and positionedclose together, so that the eye'merges the light emitted, when they arescanned, into 'a continuous color picture. An indexing system forcoordinating the intensity modulation ofthe beamwith the position of thelatter on the beam-intercepting structure is usually employed because ofbeam `scanningirregularities and `for other reasons. Theindexingsystemfhelps 'tomaintain thecolors of the reproduced image faithful tothose of the original televised scene.

One type of indexing system vthat `has "hitherto been employedinvolvesthe detection of radiant energy signals of a particularWavelength 'which are generated at Apredetermined points on the screenin 'response to the impingement of thebearn thereupon. Detection ofthese signalsmay be accomplished by placing a photosensitivedevice,responsiveto theparticular type of radiant energy'generated,insuch aposition that Whenlthe beam imping'es uponpredetermined elements ofthe screen, the device will generate electricalindexing signals `which may `be used to coordinate the beam modulation`with its "position. This coordination may be achieved eitherbyshiftingthe beam to the fproper strip or `by :modulating 1the beam witha video signal correspondingto the Vcolor of the fareaon Whichthe beamis impinging.

In the past some indexing `systems employed a photosensitive devicepositioned external to, and in front of the faceplate of the cathoderayttube. In suchla ysystem it'isipossible to deposit on the rearsurface ofthephosphor strips.anielectron-permeable layer of a reflectiveand conductive material `such as `aluminum which, `in general, servesthree purposes. MFirst, this layerhelps to increase the `brightness ofthe reproduced image by reilecting back tothe viewer-.light otherwiselost toward the rear of the phosphortscreen. Secondly, this layer, beingimpervious to ions, also obviates the-need Vfor ion traps or otherexpedients Vaimed attreducing ion spot-that`is, the 'discoloration ofthe yiluorescent screen caused by .negative `ions ipresent within .anelectromagnetically deected cathode ray tube being accelerated into`conta`ct`vvith the by the second crossover point voltage.

er ICC fluorescent screen. Thirdly, the reflective layer 'helps toincrease brightnessby enabling the uorescent screen to be maintained ata higher positive potential with respect to the cathode than would bepossible if the reflective layer Were omitted. In this latterconnection, if the iluorescent screen is oating-that is, not connectedlto a source of potential-and electrons are accelerated into impingementthereupon by a voltage which is higher than the so-called secondcrossover point of the particular phosphor used (i.e., the point atwhich the application of a higher positive potential to the screenresults in a ratio of secondary incident electrons of less than l) thepotential on the screen cannot be made more positive than the voltage ofthe second crossover point. This is due to the fact that the screen willbe charged increasingly negative by the secondaries falling back upon itso that in the latter case the attainable brightness is limited However,if a reective, conductive layer is used which is at a positivepotential, the secondary electrons, emitted in response to theimpingement on the screen of the primary electrons of the beam, arecollected by the layer so that the potential on the screen may bemaintained much'higher than if the Alayer were omitted.

Indexing systems are also known in which the photosensitive device ismounted behind the liuorescent screen. In such systems, if thereflective layer is omitted, the rear mounted photosensitive device canbe constructed to respond to light emitted by just one of the sets ofphosphor strips, but the above enumerated advantages of the reflectivelayer are lost. If it is desired, on the other "hand, to include areflective layer in such an arrangement ithas hitherto been necessary todeposit appropriate electron-sensitive indexing strips productive oflight of the wavelength to which the photosensitive device respondsontherrear surface of the reilective layer. This involves an extramanufacturing step.

`It would therefore be highly desirable, in indexing systems employingrear-mounted photosensitive devices, to arrange all of theelectron-sensitive elements, including the indexing elements, on theinner surface of the tube faceplate, and to deposit on the rear of theseelements a rellective coating of such construction that the rear-mounteddevice can be actuated in response to the scanning of the screen so asto perform the required indexing function.

Accordingly, it is an object of the invention to provide improvedsystems for reproducing images of scenes televisedtin color.

`It `is another object of the invention to provide improved screen`structures for use in television display assemblies employingphoto-indexing scanning systems in which thepho-tosensitive devices areplaced to the rear of the fluorescent screen.

`Still another object of the invention is 'to increase the intensity ofimages produced by cathode ray tube display assemblies using indexingsystems in which a rearmounted photosensitive device is employed..

Another object o-f the invention is to permit the use of a conductiveand reflective llayer in display assemblies which employ rear-mountedphotosensitive devices for indexing the scanning `position of the beamwith the intensity modulation thereof.

These objects, as `ovell as others which will appear, are achievedaccording to my invention by an improved beamintercepting structure Vforcathode ray tubes which are used with rear-mounted `photosensitivedevices to coordinatetheposition of the scanning electron beam with theintensitymodulation thereof.

'This structure comprises la number of sets fof imageproiducing phosphor`lelements respectively emissive fof radiant energy of a firstpredetermined range of wavelengths when struck by an electron beam, anda number of indexingphosphor elements which uoresce uponelectron-excitation to produce radiant energy of a second predeterminedrange of wavelengths substantially different from the first range. Allof the phosphor elements are deposited on an appropriate transparentsubstrate such as the interior surface of the faceplate of a cathode raytube. On the rear surface of the phosphor elements a layer of anelectron-permeable and conductive material is deposited which reflectsradiant energy having Wavelengths in the first range and transmits theradiant energy having wavelengths within the second range. When such astructure is embodied in a color television display tube of the typepreviously mentioned, the brightness of the image produced thereby isconsiderably enhanced and the position of the scanning electron beam maybe` signalled to the indexing system because the radiant energy emittedby the indexing phosphors, which is ordinarily chosen to be invisible tothe human eye, passes through the reective layer and impinges on thephotosensitive device mounted to the rear of the beam-interceptingstructure.

In accordance with one form of the invention as used in color televisiondisplay apparatus, a plurality of elongated, image-forrning phosphorelements vrespectively emissive of light of selected component colors ofa televised scene are deposited on the interior surface of the faceplateof a color television reproducing tube. Mixed with elements emissive oflight of one of the image colors are indexing phosphors which emitinvisible light, i.e., ultraviolet light having a wavelength orwavelengths substantially different from the light emitted by the setsof image-producing phosphors. Behind the phosphor elements and desirablyin contact therewith is deposited an electron-permeable and conductivelayer, which may be made of silver, for example, and which reflectsvisible light of the selected component image colors toward the viewerthrough the glass faceplate of the tube, and which transmits ultravioletlight emitted by the indexing phosphors toward the rear of the tube toactuate a photosensitive device responsive to the ultraviolet light. A1-ternatively, instead of mixing indexing phosphors with one set ofimage-producing phosphors, a phosphor may be chosen which emits bothvisible light of one of the selected image colors and invisible lightfor generating the indexing signals. In another form of the inventionindexing phosphors are chosen which uoresce in the infrared region, andthe electron-permeable conductive layer is constructed so as to reflectthe visible light emitted by the image-producing phosphors and totransmit the infrared light emitted by the indexing phosphors.

The sole figure is a block, schematic and partially sectional view of acolor television receiver which utilizes a cathode ray tube having abeam-intercepting structure in accordance with my invention.

Referring to the sole gure, a part of a color television receiver isshown which includes a cathode ray tube 20 incorporating abeam-intercepting structure 30 according to the present invention. Aconventional thermionic cathode 16 generates a beam 18 of electronswhich is impelled by an accelerating electrode 22 (to which a positivepotential is applied) and focussed by a focussing coil 24 positionedabout the neck of the tube 20. The focussing coil 24 is energized bycurrent from an appropriate source 26 of focussing current. The beam isdeected in response to deflection fields created by the deflection yoke28 which may be of conventional construction and which moves the beam 18in horizontal and vertical directions forming a scanning pattern. Theyoke is energized by currents supplied by the horizontal and deflectioncircuits 32. In order to mpel the beam 18 toward the beam-interceptingstructure 30 a positive potential is applied to a conductive layer 34which. is

deposited on the internal surface of the bell portion of the cathode raytube 20 as shown. A potential of about -|30 kv. is a typical value ofvoltage which may be used for this purpose.

In scanning each line the beam 18 is deflected in a direction generallytransverse to that in which the phosphor strips 46, 42 and 44 aredisposed. These strips respectively emit red, green and blue light inresponse to electrons of the beam 1S impingent thereupon. The red andblue emissive strips may be compo-sed of any conventional andappropriate phosphors for this purpose which are well-known in the colortelevision art.

In accordance with my invention the phosphor strips 44 are constructedso as to emit light of two distinct ranges of wavelengths, one visibleand the other invisible. In a preferred form of the invention as shownin the sole figure the invisible light is ultraviolet and the visiblelight isl green. In order to obtain the visible green light the strips'44 may be composed in part of the zinc orthosilicate phosphormanufactured by Du Pont under the designation of Q65-2823. When thiszinc orthosilicate phosphor is properly activated by manganese it emitsgreen light in response to electrons impingent thereupon. When zincorthosilicate is unactivated, however, it emits ultraviolet light.Therefore the strips 44 include a mixture both of activated andunactivatedzinc orthosilicate. The mixture also serves anotherpurpose-Le., the addition of unactivated zinc orthosilicate to theactivated phosphor helps to reduce the efficiency of the green emissivephosphor so as to balance its light output relative to that of the otherphosphors and thereby maintain, in the manner described and claimed incopending application of M. Sadowsky and R. E. Waggener, Serial No.364,398, led June 26, 1953, now Patent No. 2,862,- 130, proper colorvalues in the reproduced image. Alternatively the phosphor strips v44may be made from a single phosphor having two different peaks ofemission, one within the visible band of wavelengths and another Withinthe invisible. For example, the phosphor known by the Radio andTelevision Manufacturers Association designation P-15, i.e., activatedzinc oxide, peaks around 3900 A. which is near the ultraviolet regionand also at about 5000 A. which is the green region of the spectrum.

In accordance with the invention a reflective, electronpermeable layer50 of silver, for example, is deposited on the rear surface of thephosphor strips 40, 42 and 44 which helps to prevent ion spot, and whichalso tends to increase brightness by reflecting toward the viewer lightordinarily lost toward the rear of the tube and by enabling thepotential of the phosphor strips of the structure'to be more positivethan is possible withoutsuch a layer. While the layer 50 reflects red,blue and green light toward the viewer, it is essentially transparent toultraviolet light. Therefore, when the beam 18 traverses the greenemissive strips 34 containing the mixture of activated andl unactivatedzinc orthosilicate phosphor as mentioned above, the latter will emitultraviolet light, a direct ray of which is indicated by the broken line66, which will pass through the layer 50 and impinge upon therear-mounted photosensitive device 65 as shown. A window 70 is formed ina portion of the wall of the tube 20 which permits the passage ofultraviolet light of the desired wavelength. In response to the ray 66the device 65 will generate a current or a voltage which is applied tothe indexing system 72 via the leads 74. The indexing system thereuponapplies a corrective signal to the color signal processing circuits 12so that the coordination between the beam position and the beammodulation may be maintained. There are a number of particular ways `inwhich this coordination can be effected, but since this aspect of thesystem does not directly concern the present invention, furtherdescription of any particular indexing orv control system'is believedunnecessary and will be` omitted herefrom. p

If the radiant energy contained in the unactivated zinc orthosilicate isrelatively feeble, the anode layer 34 may be so Vconstructed that itreflects light in the ultraviolet region so that the other raysindicated at the number 76 will be reflected back and forth along thelayer 34 until they finally pass through the window 70 and fall upon the`photosensitive device65 in the manner explained in U.S. Patent No.2,749,449 issued to W. E. Bradley and D. E. Sunstein on June 5, 1956.

It is also possible to increase the amount of ultraviolet light whichreaches the photosensitive device 65 by making the faceplate 60 of thetube 20 of glass which reflects ultraviolet light and which transmitsred, blue and green light. This reiiected ultraviolet light will passthrough the layer 50 and will eventually impinge on the photosensitivedevice 65. This type of faceplate will also prevent stray ambientultraviolet light originating outside the tube from generating signalsin the photosensitive device 65. i

In anotherform of my-invention the layer 50 can be composed of amaterial which reflects red, blue and green light but transmits infraredrays. Within one of the phosphor strips such as the green emissive strip44 for example a phosphor material is inserted which fluoresces andemits light in the infrared region when impinged upon by an electronbeam. One such phosphor is known as P-13 and comprises magnesiumsilicate (MgSiOazMn) which emits light in the infrared region whenimpinged upon by an electron beam.

The layer 50 in this form is composed of a material which will reiiectthe Visible colors of the image and transmit infrared. The layer 50 maybe composed of silicon or germanium evaporated upon the rear surface ofthe phosphor elements. The amount of infrared radiation collected by thephotosensitive device may be increased by employing the invention taughtin the previously mentioned U.S. Patent No. 2,749,449, or by making thefaceplate 60 reliective of the infrared light and transmissive of thevisible colors. In all other respects, the operation of the tubecontaining such a beam-intercepting structure would be substantiallyidentical to the operation of the tube shown in the sole figure.

It should be appreciated that the indexing phosphor can be placedanywhere on the front side of the conductive and reliective layer, notjust in one of the phosphor strips. For example, the indexing phosphormay be inserted in spaces between selected adjoining ones of theimage-forming phosphor strips.

While the invention has been described with reference to screens forcathode ray tubes for reproduction of televised scenes in color, itshould be understood that the advantages of employing screensconstructed `according to my invention are also to be gained in cathoderay tubes for monochromatic image production in which it is desired thatthe linearity of the sweep of the electron beam, for example, beimproved by the generation of indexing signals indicative of the rate atwhich the beam traverses the screen. These indexing signals can then beused to stabilize the sweep so that the quality of the image reproducedis improved thereby.

It will be understood that still other embodiments and applications ofapparatus constructed according to my diverse forms of the inventiondescribed herein will occur to those skilled in the art. Consequently, Idesire the scope of this invention to be limited only by the appendedclaims.

What I claim is:

1. A beam-intercepting structure for a cathode ray tube comprising: aIirst electron-sensitive fluorescent portion constmcted and arranged soas to emit radiant energy within a first range of wavelengths, a secondelectronsenstive portion constructed and arranged to emit radiant energyof a second range of wavelengths substantially different'vfrom saidfirst range,` 'and a layerof a electron-permeable `material deposited onsaidv rst and second portions, said layerbeing constructed so as totransmit substantially only radiant energy having wavelengths withinsaid second range. p

2. A beam-intercepting structure for a cathode ray tube comprising: afirst electron-sensitive fluorescent portion constructed and arranged soas to emit radiant energy within a first range of wavelengths, a secondelectronsensitive portion constructed and arranged to emit radiantenergy of a second range lof wavelengths substantially different fromsaid first range, and a layer of an electrically conductiveelectron-permeable material deposited on said first and second portions,said layer being constructed so as' to transmit radiant energy havingwavelengths Wi-thin said second range.

`3. The structure according to claim 2 wherein said layer is alsoconstructed so as to reflect radiant energy having wavelengths withinsaid first range.

4. A beam-intercepting structure for a cathode ray tube comprising: aiirst electron-sensitive uorescent portion deposited upon a substrate,said first portion being constructed and larranged so as to emit lightwithin a rst range of wavelengths, a second electron-sensitive portionconstructed and arranged to emit light of a second` range of wavelengthssubstantially dilferent from said first range; and a layer of anelectrically conductive and electronpermeable material deposited uponsaid lirst and second portions, said layer being constructed so as toretlect light having wavelengths within said iirst range and toItransmit light having wavelengths within said second range.

5. A beam'intercepting structure for a cathode ray tube comprising: aiirst electron-sensitive portion constructed and arranged so as to emitvisible radiant energy within a first range of wavelengths, a secondelectron-sensitive portion constructed and arranged to emit invisibleradiant energy of a second range of wavelengths substantially diiferentfrom said lirst range, and a layer of an electrically conductive andelectron-permeable material deposited on said lirst and second portionsusaid layer being constructed so as to reflect said visible radiantenergy and to transmit said invisible radiant energy.

6. A beam-intercepting structure according to claim 5 wherein saidinvisible radiant energy is light in the ultraviolet region of thespectrum.

7. A beam-intercepting structure according to claim S wherein saidinvisible radiant energy is light in the infrared region of thespectrum.

8. A beam-intercepting structure for a cathode ray tube usedA toreproduce images of scenes televised in color, said structurecomprising: a rst electron-sensitive fluorescent portion constructed andarranged so as to emit light of selected colors, a secondelectron-sensitive portion constructed and arranged so as to emitinvisible radiant energy, and a layer of an electrically conductive andelectron-permeable material deposited on said iirst and second portions,said layer being constructed so as to reect said light and to transmitsaid invisible radiant energy.

9. In a cathode ray tube assembly for reproducing images of scenestelevised `in color, said assembly comprising a cathode ray tube and aphotosensitive device positioned to the rear of the faceplate of saidcathode ray tube which generates signals in response to a pre determinedform of radiant energy, a beam-intercepting structure for said cathoderay tube comprising: a plurality of sets of phosphor elementsrespectively emissive of selected colors in response to the impingementthereupon of said electron beam, said elements being deposited on theinner surface of said faceplate, a plurality of electrcn-sensitivefluorescent elements deposited on said faceplate constructed andarranged to emit said predetermined form of radiant energy, and a layerof an electron-permeable material deposited on the rear surface of saidelements, said layer being constructed S0 as to reect light of saidselected. colors and to transmit said predetermined form of radiantenergy. y

10. A beam-intercepting structure for a cathode ray tube, said structurecomprising: a plurality of sets of electron-sensitive tluorescentelements deposited on the inner surface of said faceplate, one of saidsets of elements comprising a phosphor which has a radiant energyemission characteristic having peaks at two different wavelengths, and alayer of an electron-permeable and conductive material deposited on saidelements which transmits radiant energy of only one of said wavelengths.11. The structure according to claim 10 wherein said layer reflectsradiant energy of the one of said `two wavelengths which is nottransmitted by it.

12- A beam-intercepting structure for a cathode ray tube used toreproduce images of scenes televisedfin color, said structurecomprising: a plurality of sets of elongated, electron-sensitivephosphor strips deposited on a substrate, said sets of stripsrespectively being emissive of light of the additive primary colorcomponents of said televised scene when traversed by an electron beam,the material of one of said sets of strips also being emissive ofdetectable invisible light when traversed by an electron beam, and alayer of an electron-permeable and conductive material deposited on saidstrips which reects said colors Vand transmits said invisible light.

. color components of s aid televised scene, one of said sets of stripsalso containing material which emits de- |tectable invisible light whentraversedl by an electron beam, and a layer of an electron-permeable and'conductive material deposited on such strips which reects said colorsand transmits said invisible light.

15. A beam-intercepting structure according to claim 14 in which saidinvisible light is inthe ultraviolet regon of the spectrum and saidlayer comprises silver particles.

References Cited in the tile of this lpatent UNITED STATS PATENTSsziklai Mar. 6, 1956 Wallmark Dec. 18, 1956 n Mlm

1. A BEAM-INTERCEPTING STRUCTURE FOR A CATHODE RAY TUBE COMPRISING: AFIRST ELECTRON-SENSITIVE FLUORESCENT PORTION CONSTRUCTED AND ARRANGED SOAS TO EMIT RADIANT ENERGY WITHIN A FIRST RANGE OF WAVELENGTHS, A SECONDELECTRONSENSITIVE PORTION CONSTRUCTED AND ARRANGED TO EMIT RADIANTENERGY OF A SECOND RANGE OF WAVELENGTHS SUBSTANTIALLY DIFFERENT FROMSAID FIRST RANGE, AND A LAYER OF AN ELECTRON-PERMEABLE MATERIALDEPOSITED ON SAID FIRST AND SECOND PORTIONS, SAID LAYER BEINGCONSTRUCTED SO AS TO TRANSMIT SUBSTANTIALLY ONLY RADIANT ENERGY HAVINGWAVELENGTHS WITHIN SAID SECONDD RANGE.